Apparatus and method for drying particulate matter



Nov. 2, 1965 F. B. oA'rEs r-:TAL 3,214,844

APPARATUS AND METHOD FOR DRYING PARTICULATE MATTER Filed Dec. ll, 1961 5 Sheets-Sheet 2 INVENTORS B. GATES E. RAHM A. KELLEY A. DANKO md5/ul from.

ATTORNEYS Nov. 2, 1965 F. B. oA'rEs ET AL APPARATUS AND METHOD FOR DRYING PARTICULATE MATTER Filed Dec. ll, 1961 5 Sheets-Sheet 3 INVENTORS FRANCIS B. HOWARD E. GILBERT A. EMERY A. DANKO KELLEY AT TOR N EYS United States Patent Oli ice 3,214,844 APPARATUS AND METHOD PGR DRYING PARTICULATE MATIER Francis B. Gates, Howard E. Rahm, and Gilbert A. Kelley, Toledo, Ohio, and Emery A. Danko, Lambertville,

Mich., assignors to Midland-Ross Corporation, Toledo,

Ohio, a corporation of Ohio Filed Dec. 11, 1961, Ser. N 158,268 8 Claims. (Ci. 34-10) This invention relates to a dryer, and more particularly to a dryer for rapidly drying particles, e.g., of cereal, at a relatively higher temperature, for example, at one suiiiciently high to cause toasting of cereal particles.

Heretofore, a number of methods and apparatuses have been used for drying various types of particles. However, most of the techniques heretofore known for drying particles have been incapable of providing close control over the length of time the particles are subjected to the drying medium. When relatively low temperatures are employed, variations in the drying time are unimportant; however, the drying time can be critical when higher temperatures suicient to etect other changes in the particles, in addition to the removal of moisture, are employed. This is true, for example, when higher temperatures are used in drying cereal particles to toast the particles and thereby to improve the taste and color. Still higher temperatures are sometimes used to cause the cereal particles to expand rapidly or puff. Drying time is also critical when higher temperatures are used to enable a greater number of particles to be dried in a shorter length of time in order to reduce the overall process time, to reduce the size and cost of the drying apparatus, and to reduce the amount of floor space.

Relatively high temperatures are frequently used to accomplish the above results. As a consequence, a variation of only one or two seconds in the length of time the particles are subjected to the heated drying medium will cause signicant differences, eg., in color and taste of cereal particles. Variations of more than one or two seconds are common with present drying apparatuses and methods.

The present invention provides an improved method and apparatus for drying particles for closely controlled periods of time. This is accomplished by transporting the particles in at least partially physically-separated groups laterially through a heated air stream at a constant rate to assure that each group will be in the stream for a fixed length of time. In one preferred form of apparatus embodying the principles of the invention, the cereal particles are transported through the air stream in perforated compartments, several of which are aflixed to a conveyor chain and are moved sequentially through the stream in a straight line. The air passes upwardly through the compartments at a velocity suflicient to move the particles therein and to maintain them 1n motion, and preferably suspended above the perforated bottom. As a consequence, drying is accomplished more effectively. In one embodiment of the invention, a separate mesh belt is located above the compartments and extends parallelly to the chain to which the compartments are attached, being driven in synchronization therewith. The lower run of the mesh belt contacts the tops of the compartments when within the air stream to prevent the blowing of particles from the compartments, but is spaced from the compartments on both sides of the air stream so that the compartments are uncovered for loading and unloading. In another preferred form, the compartments expand outwardly and upwardly from the bottoms so that the air velocity therethrough is an inverse function of the distance above the bottom; in this case all the particles can be suspended above the compartment bottoms by an 3,2%,844 Patented Nov. 2, 1965 air flow which is insufficient to carry the particles out the compartment tops. In still another preferred form the apparatus comprises a trough-like member with a perforate bottom, sidewalls which expand upwardly and outwardly and a screw-conveyor to advance the particles through the trough-like member. In this case, the air velocity is controlled to suspend the particles in the effective zone of the conveyor, so that required residence times are provided.

It is, therefore, a principal object of the invention to provide an improved method and apparatus for removing moisture from particles.

Another object of the invention is to provide a method and apparatus for subjecting particles to a drying medium for more uniform, closely controlled periods of time.

Still another object of the invention is to provide a method and apparatus for the rapid removal of moisture from particles, and at relatively high temperatures.

A further object of the invention is to provide drying apparatus in which particles are divided into a plurality of groups which are at least partially separated from one another physically, and in which the groups of particles are advanced through the apparatus with little or no intermixing.

Other objects and advantages of the invention will be apparent from the following detailed description of preferred embodiments thereof, reference being made to the accompanying drawings, in which:

FIG. I is a fragmentary view in longitudinal, vertical cross section, taken along an oiset line 1 1 of FIG. 2, of a dryer embodying the principles of the invention;

FIG. 2 is a view in lateral, vertical cross section, taken along the line 2 2 of FIG. l;

FIG. 3 is a view in perspective of a compartment etnployed with the dryer shown in FIGS. 1 and 2;

FIG. 4 is a View in vertical cross section of a portion of the dryer of FIGS. l and 2;

FIG. 5 is a view in cross section taken along the line 5 5 of FIG. 4; and

FIG. 6 is a view in perspective of a modification of the dryer shown in FIG. 3.

Referring to the drawings, and more particularly to FIGS. 1 and 2, a dryer embodying the principles of the invention is indicated generally at 10 and includes insulated side, end, top and bottom walls 12, 14, 16 and 18, respectively, and supporting legs 20. The dryer 10 is divided into three sections or zones 22, 24, and 26. The temperature and velocity of the air or other drying medium in each zone or section is regulated individually.

Individual control of the three sections enables more heat to be added to the air in the first stage where the moisture content is highest, for example. It also enables higher velocity air to be used in the first stage where the particles are the heaviest, because they contain the most moisture. In many instances, however, all three ol' the streams are maintained at the same temperature and velocity.

The three sections 22-26 (see FIG. 2 in particular) are substantially identical, each including a combustion chamber 28, a burner 30, a connecting duct 32, a blower housing 34 with a blower 36, a supply passage 38, a screen 40, and a return passage 42. The burner 30 is supplied with air and fuel through lines 44 and 46 which can be regulated to vary the output of the burner 30 and the temperature of the air circulated in the associated one of the sections 22-26. The blower 36 in the housing 34 is driven by a variable speed motor 48 which can be regulated to change the speed of the blower 36 and the velocity of the air in the associated section. Thus, both the temperature and the velocity 'of air in each section can be regulated relatively easily, as required.

The screen 40 between the supply passage 38 and the return passage 42 helps distribute the air uniformly laterally of the passages and enables more uniform upward ow. When the air again enters the combustion chamber 28, it is reheated by the burner 30 and makeup air is supplied through the burner 30 from the air line 44. The burner 30 preferably is an excess-air type of burner which receives a quantity of air substantially in excess of the quantity necessary to provide a stoichiometric airfuel ratio.

Rails 50 cross intermediate portions of all three of the passages 42, one of the rails 50 being afxed to one of the side walls 12 and the other being aiiixed to a partition 52 which separates the passages 38 and 42. These rails extend from a charge opening 53 (FIG. 1) to a point somewhat beyond a discharge opening 54. Rollers 55 (see FIG. 3, particularly) are pinned to links 56 of a conveyor chain and to brackets 57 on opposite ends 'of receptacles 58. The rollers 55 ride lupon the rails 50 (FIG. l) and carry the receptacles 58 laterally through the streams of air in the three sections 22-26. The conveyor chains made up of the links 56 carry the receptacles 58 around a 4drive sprocket 60 driven by a suitable motor and reducer combination 62, through a return trough 64, and around an idler sprocket 66. In the return trough 64 the rollers 55 of the chain 56 ride on top of supporting rails 68 (FIG. 2) to support the receptacles 58 in their inverted positions.

Each of the receptacles 58 includes a perforate bottom wall 70 (FIG. 3) having a plurality of closely and uniformly spaced perforations or openings 72 which extend to the periphery of the bottom 70 to prevent the possibility of any dead space between the openings 72 and side walls 74 and 76 or end walls 78 and 80. The receptacles 58 are spaced closely enough together (see FIG. l) that the rear wall 74 of one receptacle is substantially contiguous with the front wall 76 of an adjacent receptacle. When two receptacles are so positioned, with substantially contiguous front and rear walls, a forwardly extending ange 82 (FIG. 3) of the front wall 76 of the one receptacle overlaps a forwardly extending llange 84 of the rear wall 74 of the other. This provides a relatively air-tight connection between the adjacent receptacle 58. In addition, the end walls 78 and 80 have laterally-extending flanges 86 and 88 cooperating with longitudinal sealing anges 90 (FIG. 2) which are located above and parallel to the rails 50 and extend from the charge opening 53 to the discharge opening 54. The cooperation between the lateral anges 86 and 88 and the longitudinal sealing flanges 90 provides a substantially air tight seal between the receptacles 58 and the outside wall 12 and between the receptacles 58 and the partition 52. Hence, substantially all of the hot air or other drying medium entering the lower part of the passage 42 will pass through the perforations 72 and through the receptacles 58.

Because the velocity of the air passing through the perforations 72 is sucient to move and keep in motion cereal in the receptacles 58, a possibility exists that some of the particles which tend to be lighter or to present larger surfaces than others would be blown completely out of the receptacles. To prevent this from happening, a mesh belt 92 is located above the receptacles 58 with the lower run of the belt 92 in contact with the upper edges of the adjacent receptacles 58 to constitute pervious covers therefor. The belt 92 is driven in synchronization with the receptacles 58 by suitable mechanism 94 (FIG. 1) mechanically connecting the chain 56 with the belt 92. The belt 92 is thus driven through a drive roller 96 and travels around suitable idlers 98. To prevent the possibility of the mesh belt 92 being blown upwardly and separated from the receptacles 58, two hold-down bars 100 extend longitudinally of the dryer 10 near the lateral flanges 86 and 88 of the receptacles 58 and just above the lower run of the belt 92. The hold-down bars are supported through rods 102 (FIG. 2) by brackets 104.

The receptacles 58 at the charge end of the dryer 10 are not encumbered by the mesh belt 92. As a consequence, they can be loaded easily from a suitable feed hopper 106 (FIG. 1). If desired, the hopper 106 can feed cereal continuously to the receptacles as they pass thereunder. A ilexible flap 108 is provided to push any cereal off the flanges 82 and 84 between the receptacles 58. The receptacles 58 are also unencumbered at the discharge end so that the cereal can be discharged directly into a suitable container (not shown) located below the drive sprocket 60.

By way of further illustration, a specic example is set forth below. Cereal particles in the form .of flakes having a diameter of .approximately 57s inch and a thickness of :approximately 1/16 inch were placed in the recepta-cless 58 to a depth of only about 1A inch, equal to a loading of approximately 0.2 pound per square foot, although the overall height of the receptacles 58 was about 8 inches. The openings 72 in the bottoms 70 of the receptacles 58 were of 0.098 inch diameter on 1A inch centers so that the bottoms 70 were approximately 14 percent open. Air in the combustion chamber 28 of each of the sections 22-26 was heated to 550 F. and -was blown down the passage 38 at a velocity of 800-900 feet per minute. The air at the openings 72 had a velocity of 3500 feet per minute but decayed rapidly to a velocity of about 400 feet per minute at a distance about 3A inch above the openings. The pressure drop across the receptacles 58 was 1.1 inches water column. rPhe :chain 56 .and the receptacles 58 traveled through the three sections 22-26 at a speed such that the residence time of the receptacles within the three sections was 'only 81/2 seconds. It was found that either an increase or a decrease in this time Iof less than one second produced a noticeable variation in the quality of the particles. The finished particles had 21/2-3 percent moisture, reduced yfrom 15 per-cent moisture originally. Optimum results have been achieved when the volume of the particles have ranged from about 1 percent to about 10 percent of the total volume of the receptacles. In such case, physical yseparation of the individual particles can be achieved.

In this instance, the particles not only had to be dried, but also toasted and puffed. To accomplish these three results, the relatively high 550 F. temperature was necessary, although toasting alone could be accomplished at a lsomewhat lower temperature and drying alone could be accomplished at a much lower temperature. The higher temperature, however, also enabled rapid drying and high production in a relatively small space, and with relatively small apparatus.

lDuring the drying process, a number of the particles blew against the mesh belt 92 and stayed there during -most of the process. Such particles did not inhibit the How of air through the compartment, however, unless they exceeded about 30 percent of lthe total.

Another embodiment of the invention is shown in FIGS. 4 and 5 and includes a dryer which is substantially the same as the dryer 10 of FIGS. 1 and 2, and, therefore, is not illust-rated in detail. The dryers differ basically only in the conveying means employed to transport the cereal particles in physically-separated groups laterally through the air stream established by the blower 36. In this instance, the conveying means includes parallel troughs 110 `which extend longitudinally through the dryer and beyond the end walls 14. A conveying screw 112 located in each 4of the troughs 110 is driven by a suitable motor 114 at one end of the trough 110, and is supported by bearing blocks 116. As the screw 112 is rotated, it carries -cereal particles supplied from a hopper 118 through the trough 110.

The trough 110 includes a bottom 120` having perforations 122 therein which are closely and uniformly spaced to prevent the possibility of any dead space in the bottom 120. The trough 110 has slanted side walls 124, so that its cross-sectional shape is similar to a symmetric trapezoid. By slanting the side Walls, rather than placing them in a perpendicular position, the horizontal cross-sectional area of the trough 110 increases from the 'bottom 129 to the top thereof. As a consequence of the increase in cross-sectional area, the lineal velocity of the air decreases rapidly, and can be easily controlled to enter the perforations 122 at a velocity sufiiciently high to suspend the particles above the bottom 120 and yet to exit from the top of the trough 110 at a velocity sufiiciently low that it will not carry the particles therefrom. Because of the control afforded by the slanted side Walls 124, no top whatsoever is needed on the trough 110. In addition, a higher proportion or all of the particles are continuously suspended above the bottom 120. The slanted side walls also enable a reduction in the total volume of air needed for suspension and in the total horsepower consumption. Further, fewer modification of the equipment are necessary to accommodate different sizes and shapes of cereal or other particles.

The conveying screw 112 can be of any suitable design and includes a helical wall or flange 126 and a central shaft 128. The helical wall 126 provides separating means by which `the particles in the trough 114i are partially but effectively physically separated into groups as they are carried laterally through the air stream. The periphery of the helical Wall 126 is quite close to the bottom 12) and to the slanted side walls 124 and can be made even closer by curving the bottom 120, the side walls 124, or both. However, it is preferred that the air passing through the perforations 122 suspend the particles above the bottom 120 so that the helical Wall 125 provides sufficient physical separation without curvature of the various walls.

The advantages accomplished by slanting the side Walls of the trough 119 can also be attained with the dryer of FIGS. 1 3 by slanting the walls of the receptacle 5S. A receptacle 136 of FIG. 6 is modified in this manner, having slanted side walls 138 and 140 and trapezoidal end walls 142 and 144. The receptacle 136 is like the receptacle 57 in that it has a perforate bottom and iianges to reduce the by-passing of air.

It will be noted that the dryers according to the invention all maintain cereal or the like to be dried in a plurality of at least partially separated groups and advance the groups, while so separated, laterally through a stream of a drying medium. In the apparatus of FIGS. 1 3, or modified by substitution of the receptacle 136 of FIG. 6, the separation is complete, but in the apparatus of FIGS. 4 and 5 the separation is partial. In all instances, however, the separation is effective to control the residence times of the particles within the narrow limits that are necessary to accomplish rapid and controlled drying, roasting, or both. For optimum results the individual particles in each of the groups are also physically separated from one another by suspension in the stream of the drying medium. 1n all instances this can be accomplished most effectively and eiciently when the volume of the enclosures, Whether partial -or complete, is from about l() to about 100 times the volume of the particles enclosed therein.

Various modifications of the above described embodiments of the invention will be apparent to those skilled in the art. Such modifications can be made without departing from the spirit and scope of the invention, as defined in the appended claims.

We claim:

1. A method of drying particles, comprising the following steps:

(a) introducing the particles to a drying chamber in substantially physically separated groups;

(b) conveying said groups through said chamber at a substantially constant speed;

(c) establishing a flow of a stream of drying medium;

(d) simultaneously suspending substantially all of the particles in each of said separated groups in said stream in said chamber by passing said stream of drying medium upwardly and simultaneously through the entire bottom region of each of said groups at a velocity sufficient to maintain simultaneous suspension of substantially all particles in each of said groups in said stream while maintaining physical separation of said groups of particles.

2. The method according to claim 1 further comprising reducing the velocity of said stream of drying medium as it is passed upwardly through said groups of particles.

3. Apparatus for continuously drying particles comprising, in combination:

(a) wall means forming a substantially horizontally extending drying chamber having first and second adjacent and aligned zones;

(b) means for conveying said particles through said drying chamber said conveying means including second wall means forming a plurality of open top receptacles in which the particles are conveyed in physically separated groups therein, and said second wall means including bottom wall means perforate over substantially its entire extent thereby being pervious to a gas, and at least one pair of opposed walls attached to said bottom wall means and continuously diverging from each other from the bottom wall means to substantially the top of said receptacles;

(c) means for establishing ows of first and second streams of gaseous drying mediums; and

(d) means for directing said first and second streams simultaneously through substantially the entire bottom wall means, upwardly through said tirst and lsecond zones respective lof the drying chamber, the velocities suihcient to cause and maintain suspension of substantially all particles in said first and second streams during substantially the entire time that the particles are being conveyed through said drying chamber.

4. Apparatus according to claim 3 further comprising first and second heating means for heating said first and second streams of gaseous drying mediums respectively before passage of the stream through said first and second zones.

5. Apparatus for continuously drying particles cornprising in combination:

(a) means for conveying said particles in a generally horizontal path, said conveying means including wall means forming a plurality of open top receptacles in which the particles are conveyed in physically separated groups along said generally horizontal path, said wall means including bottom wall means perforate over substantially its entire extent, there- `by being pervious to a gas, and said wall means further including at least one pair of opposed walls attached to said bottom wall means and continuously diverging from each other from the bottom wall means substantially to the top of the receptacles within which said particles are adapted to be contained;

(b) means for actuating said conveying means to move saicl1 particle receptacles in said generally horizontal Pat (c) means for establishing a flow of a stream of a gaseous drying medium; and

(d) means for directing the stream simultaneously through substantially the entire bottom wall means at a velocity sufficient to cause and maintain suspension of substantially all the particles in said stream during substantially the entire time that the particles are being conveyed along said horizontal path.

6. Apparatus according to claim 5 wherein said conveying means comprises a screw conveyor extending through said chamber and said wall means formmg said plurality of open top receptacles comprises:

(a) successive turns of said screw conveyor which form side walls of said receptacles; 5

(b) the pair of diverging opposed walls which extend from and are attached to said bottom Wall means, extend the entire length of said screw conveyor and form end walls of said receptacles.

7. Apparatus according to claim 5 wherein said wall l0 means forming said plurality of open top receptacles comprises:

(a) opposed pairs of end walls, each pair being connected to a separate bottom portion of the bottom wall means and extending upwardly therefrom;

(b) opposed pairs of side walls, each pair being connected to a bottom portion to which a pair of end walls are attached and continuously diverging from each other and from said bottom portion and being connected to said pair of end walls.

8. Apparatus for continuously drying particles comprising, in combination:

S `other from the bottom Wall means; said bottom wall means, pair of opposed side walls and successive turns of said screw conveyor being effective to separate the particles to be dried into a plurality of substantially physically separated receptacles;

(c) means for turning said screw conveyor to advance said receptacles through said chamber in a generally horizontal path;

(d) means for establishing a ow of gaseous drying medium; and

(d) means for directing the stream simultaneously through substantially the entire bottom wall means at `a velocity sufiicient to cause and maintain suspension of substantially all the particles in said stream during substantially the entire time that the particles are being conveyed along said horizontal path.

References Cited bythe Examiner UNITED STATES PATENTS 80,578 8/68 Waterhouse 34-2l8 1,707,929 4/29 Bennett 34-31 2,044,744 6/36 Hansen 34-10 X 2,067,115 1/37 Bogaty 34-236 2,249,152 7/4'1 Marshall 34-l0 X 2,559,551 7/51 Weber 34-10 X 2,777,212 1/57 McOmber 34-215 2,899,189 8/59 Matis 34-216 FOREIGN PATENTS 547,619 10/57 Canada.

WILLIAM F. ODEA, Primary Examiner.

NORMAN YUDKOFF, Examiner. 

1. A METHOD OF DRYING PARTICLES, COMPRISING THE FOLLOWING STEPS: (A) INTRODUCING THE PARTICLES TO A DRYING CHAMBER IN SUBSTANTIALLY PHYSICALLY SEPARATED GROUPS; (B) CONVEYING SAID GROUPS THROUGH SAID CHAMBER AT A SUBSTANTIALLY CONSTANT SPEED; (C) ESTABLISHING A FLOW OF A STREAM OF DRYING MEDIUM; (D) SIMULTANEOUSLY SUSPENDING SUBSTANTIALLY ALL OF THE PARTICLES IN EACH OF SAID SEPARATED GROUPS IN SAID STREAM IN SAID CHAMBER BY PASSING SAID STREAM OF 